Thursday, June 14, 2012

I know what you're thinking ... we haven't even reached the official start of summer. And here I am, talking about winter.

But I've received two emails in the past week from people in the meteorology industry, discussing what might be ahead for the winter of 2012-13 across North America.

The consensus is that it'll be colder than last winter, but you don't have to be a genius to predict that. The winter of 2011-12 was among the mildest on record. And if it hadn't been for a bit of sleet on a Sunday night in February, Charlotte would have logged its first snow-free winter on record.

But most meteorologists predict at least a weak El Nino condition this winter, and that bears watching.

We're coming off two straight La Nina winters, with cooler-than-average waters in the eastern Pacific Ocean. La Nina winters tend to be dry and warm in the South. In the winter of 2010-11, La Nina was overwhelmed from December to mid-February by another factor -- a strongly negative Arctic Oscillation (AO). That brought very cold air into the East.

But the latter stages of the winter were mild, as La Nina took over.

The past winter featured La Nina and a positive AO. The jet stream kept cold air in the far northern latitudes, which meant a cold winter for Alaska. It also meant the Greenland Block (high pressure over Greenland, which steers cold air into the eastern U.S.) did not develop.

El Nino winters tend to be chilly and wet in the Southeast. That's especially true of strong El Nino winters. But most meteorologists seem to be talking about a weak to moderate El Nino event.

"Based on what the patterns we are already seeing over the Pacific Ocean, we believe that an El Nino is beginning to set up, and we may have a weak El Nino signature by late in the summer," said Paul Pastelok, long-range forecaster for AccuWeather.

That would point to less-than-average tropical storm and hurricane activity in the Atlantic and Caribbean.

But its impact on winter is less certain, since the El Nino condition might be weak. That would mean a good chance of a wet winter, but the Carolinas might be on the battle lines of cold and warm air. Incidentally, Pastelok says weak El Nino winters typically bring lots of snow to New York City, Philadelphia and Chicago.

A lot of it will depend on the Arctic Oscillation. I doubt that any meteorologist expects a repeat of last winter, so it stands to reason that the AO will go negative at times this year. With El Nino moisture around, that points to a good chance that more typical Carolinas winter weather -- that is, the occasional threat of snow and ice -- are pretty much a certainty.

About this blog

Steve Lyttle says growing up in northeastern Ohio, with its foot-deep snows and summertime severe thunderstorms, fueled his interest in meteorology. He has written about weather for 10 years at The Observer. Join the discussion about weather trends and weird weather events -- whether local or around the world.